New node not getting added

Hii I am trying to add a new node with elasticsearch version 2.2.0 to my existing cluster that contains only single node with elasticsearch version 2.1.0 . I got to know that its possible to mix these two versions. Now When I do curl -XGET 'http://localhost:9200/_nodes' I don't see the newly added node . This clearly means my new node has not been added right ? So what can be the reason for this ?

Is there any particular reason you are not using the same version? It might not be the cause now but as you scale up ELK it could cause problems down the road.

Also what is your set-up like? Did you define your "localhost" as the "master node"?

@w0lverine I tried to upgrade the node using this link -
I lost my old logs probably because I did not stop the node during upgradation . Am I right ? I just did step 3 because my cluster has only one node. Am I right in thinking so ??

Yes I wouldn't skip around the documentation and do steps out of order unless you know what you are doing. Start from
step 1: disable shard allocation
step 2: go ahead and stop non-essential indexing(if you are able too)
step 3: stop and upgrade single node

If you suddenly stop the node it will not replicate the shards that were being processed during the time of the node shutdown. Hence why disable shard allocation before shutdown of node.